Compile warnings fixes in deep_mind.cpp, abi_serializer.cpp, producer_plugin.cpp, auth_tests.cpp

[linh2931]

Resolve #20

Fix following compile warnings:

libraries/chain/deep_mind.cpp:46:4: warning: control reaches end of non-void function [-Wreturn-type]

libraries/chain/abi_serializer.cpp:80:42: warning: ‘void eosio::chain::abi_serializer::set_abi(const eosio::chain::abi_def&, const fc::microseconds&)’ is deprecated: use the overload with yield_function_t[=create_yield_function(max_serialization_time)] [-Wdeprecated-declarations]

plugins/producer_plugin/producer_plugin.cpp:1959:43: warning: comparison of integer expressions of different signedness: ‘uint64_t’ {aka ‘long unsigned int’} and ‘int64_t’ {aka  ‘long int’} [-Wsign-compare]
 1959 |                if( prev_billed_plus100_us < max_trx_time.count() ) max_trx_time = fc::microseconds( prev_billed_plus100_us );

unittests/auth_tests.cpp:235:18: warning: variable ‘new_owner_priv_key’ set but not used [-Wunused-but-set-variable]

[heifner]

This is narrowing from uint64_t to int64_t which should be fine here as prev_billed_cpu_time_us is uint32_t. BTW, this is a very odd way to multiple a value by 2. It is written this way because originally we had a different value than 100.

[linh2931]

Thanks for the review. Yes, I was worried about that narrowing too. Since fc::microseconds's _count is defined as int64_t, it should fine.